"i really do not want to spend more than $500 for the speakers"
There are many excellent front ported speakers available in this price range right now:
Wharfedale Diamond 9.2 - discontinued but available from Internet dealers for under $300 new, or much less used, great all-rounder
Usher S-520 - $479/pr. new, good for rock
B&W 685 - $650/pr. new, another alternative could be a used pair of old English built B&W 601's or 602's, preferably S2 or S3 designation, for much much less than $500 used
PSB Image B15 - $379 new, another good all rounder
Paradigm Titan v.5 - under $400 new from Internet dealers, almost full range
Monitor Audio Bronze BR2 - $450 new, sound expensive
Epos ELS3 - $399 new, not front ported but sound really, really good.
These are all very competent speakers and I think would pair well with the Decco for near wall placement. Many of these are the larger version of the companies' bookshelf speakers because it is difficult to squeeze a port on the face of a smaller speaker. While these larger "bookshelf" speakers will be more efficient, most of these boxes are pretty deep - something to consider if attempting to actually place on any bookshelf less than 12" deep. If space is a serious issue, I might recommend the Epos ELS3 or the Paradigm Atom Monitor in place of the company's Titan.
Good luck.